utils: etree to dict translation reorganization

* Adds xmlhelpers to utils to handle custom XML.

Signed-off-by: Pedro Gaudêncio <pedro.gaudencio@cern.ch>
Reviewed-by: Javier Martin Montull <javier.martin.montull@cern.ch>
utils: import json from arxiv api

* Adds API to import JSON data from http://export.arxiv.org with a
  given ArXiv ID.

Signed-off-by: Pedro Gaudêncio <pedro.gaudencio@cern.ch>
Reviewed-by: Javier Martin Montull <javier.martin.montull@cern.ch>
arxiv: initial Flask extension commit

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
records: API for database querying with DOI

* Adds API to query the database with a DOI.

Signed-off-by: Pedro Gaudêncio <pedro.gaudencio@cern.ch>
Reviewed-by: Javier Martin Montull <javier.martin.montull@cern.ch>
Reviewed-by: Jiri Kuncar <jiri.kuncar@cern.ch>
travis: less verbose output

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
restful: addition of RestValidator

* Adds a custom validator for restful api.

* Adds a dictionary of validation errors
  for the RestValidator.

Signed-off-by: Konstantinos Kostis <konstantinos.kostis@cern.ch>
messages: addition of REST API

* Adds an errors class for the messages
  restful api.

* Adds a MessageValidationError class to the errors.

* Adds an error handler for the messages
  restful api.

* Tests the messages restful api.

* Fixes the imports and use of configuration
  variables.

Signed-off-by: Konstantinos Kostis <konstantinos.kostis@cern.ch>